The present invention relates generally to wireless communication devices and more specifically to a method and apparatus for causing a wireless communication device to detect activation of semi-persistent scheduling (SPS) resources.
As used herein, the terms “user agent” and “UA” can refer to wireless devices such as mobile telephones, personal digital assistants (PDAs), handheld or laptop computers, and similar devices that have telecommunications capabilities. In some embodiments, a UA may refer to a mobile, wireless device or other user equipment (UE). The term “UA” may also refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station or access device transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an E-UTRAN (evolved universal terrestrial radio access network) node B (eNB), a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). As used herein, the term “access device” can refer to any component, such as a traditional base station or an LTE eNB (Evolved Node B), that can provide a UA with access to other components in a telecommunications system.
In mobile communication systems such as E-UTRAN, the access device provides radio access to one or more UAs. The access device comprises a packet scheduler for allocating uplink and downlink data transmission resources amongst all the UAs communicating with the access device. The functions of the scheduler include, among others, dividing the available air interface capacity between the UAs, deciding the resources (e.g. sub-carrier frequencies and timing) to be used for each UA's packet data transmission including uplink and downlink, and monitoring packet allocation and system load. The scheduler allocates physical layer resources for downlink shared channel (PDSCH) and uplink shared channel (PUSCH) data transmissions, and sends scheduling information to the UAs through a physical downlink control channel (PDCCH). The UAs refer to the scheduling information for the timing, frequency, data block size, modulation and coding of uplink and downlink transmissions.
Several different downlink control information (DCI) message formats are used to communicate resource assignments to UAs including, among others, a DCI format 0 for specifying uplink resources and DCI formats 1, 1A, 2 and 2A for specifying downlink resources. Uplink-specifying DCI format 0 includes several DCI fields, each of which includes information for specifying a different aspect of allocated uplink resources. Exemplary DCI format 0 DCI fields include a transmit power control (TPC) field, a cyclic shift demodulation reference signal (DM-RS) field, a modulating coding scheme (MCS) and redundancy version field, a New Data Indicator (NDI) field, a resource block assignment field and a hopping flag field. The NDI field may be a single bit field that has a value of either 0 or 1. If the DCI message indicates that new data is to be transferred using an established resource, the value of the NDI field may be toggled (i.e., from 0 to 1, and vice versa) from its previous value. By toggling the value of the NDI field, the DCI message indicates to the UA that new data is being transferred.
The downlink specifying DCI formats 1, 1A, 2 and 2A each include several DCI fields that include information for specifying different aspects of allocated downlink resources. Exemplary DCI format 1, 1A, 2 and 2A DCI fields include a Hybrid Automatic Repeat reQuest (HARQ) process number field, an MCS field, a New Data Indicator (NDI) field, a resource block assignment field and a redundancy version field. Each of the DCI formats 0, 1, 2, 1A and 2A includes additional fields for specifying allocated resources. The access device selects one of the downlink DCI formats for allocating resources to a UA as a function of several factors including UA and access device capabilities, the amount of data a UA has to transmit, the amount of communication traffic within a cell, etc.
After a DCI formatted massage is generated, an access device may generate a cyclic redundancy check (CRC) for the message and append the CRC to the DCI formatted message. Next, the access device may use a Cell-Radio Network Terminal Identifier (C-RNTI) or Semi-Persistent Scheduling Radio Network Terminal Identifier (SPS-RNTI) that is uniquely associated with a UA to scramble the CRC prior to transmitting the message to the UA. When the message is received at the UA, the UA calculates the CRC from the received message, uses the C-RNTI or SPS-RNTI to scramble the CRC and uses the scrambled CRC to ascertain whether the message was received accurately. If the CRC check indicates that the message was not intended for the UA (i.e. the CRC derived at the UA does not match the CRC attached to the received message), the UA may ignore the message.
In communications between an access device and a UA, HARQ is a scheme for re-transmitting a traffic data packet to compensate for an incorrectly received traffic packet. A HARQ scheme is used both in uplink and downlink transmissions in LTE systems. Take downlink transmissions for example. For each downlink packet received by a UA, a positive acknowledgment (ACK) is transmitted on a Physical Uplink Control Channel (PUCCH) from the UA to the access device after a cyclic redundancy check (CRC) performed by the UA indicates a successful decoding. If the CRC indicates a packet is not received correctly, a UA HARQ entity transmits a negative acknowledgement (NACK) on the PUCCH in order to request a retransmission of the erroneously received packet. Once a HARQ NACK is transmitted to an access device, the UA waits to receive a retransmitted traffic data packet. When the HARQ NACK is received at an access device, the access device retransmits the incorrectly received packet to the UA. This process of transmitting, ACK/NACK and retransmitting continues until either the packet is correctly received or a maximum number of retransmissions has been reached.
Whenever control information has to be transmitted between an access device and a UA, the resources required to complete that transmission cannot be used to transmit other information such as voice or application information and data. For this reason, it is important to minimize the amount of control data required for controlling communications between and access device and a UA.
Two general types of communication scheduling for minimizing control data include persistent and semi-persistent scheduling. In persistent scheduling, as the label implies, communication resources are pre-allocated for a specific UA until released regardless of whether the resources remain in use during an entire scheduled period. For simple persistent scheduling, persistently scheduled resources are not available to other UAs for communication, even when the UA to which the persistent resource is assigned does not use the resource.
In semi-persistent scheduling (SPS), however, a resource may be assigned to a UA and used on an on-going basis until the access device decides to stop using the resource and instructs the UA to stop using the resource. Thus, for example, in the case of Voice over Internet Protocol (VoIP), a typical communication sequence may include interleaved “talk spurt states” and “silence states” where data corresponding to a UA user's speech is communicated during talk spurt states and no data except comfort noise information is communicated during silence states.
In some implementations, for example, during a talk spurt state, VoIP packets arrive at a fixed rate such as one packet every 20 ms with only minimal variation in packet size. In that case, SPS activation may be used to assign reoccurring downlink and uplink SPS resources (e.g., as an initial grant) during the talk spurt state. During times of UA inactivity (e.g., silence states), however, the allocated uplink and downlink resources associated with a UA may be released so that the resources can be allocated to other UAs. As such, the uplink and downlink resources are persistently allocated only in the sense that the resources remain allocated at long as the resources are being actively used to communicate information. Once resource use ceases, the resources may be released. After the resources are released, when a next talk spurt is to occur, the access device transmits one or more additional DCI formatted messages to the UA to commence a new SPS resource allocation to support the next spurt. Hereafter the phrase “SPS resources” can be used to refer to resources that are semi-persistently scheduled. In order to control SPS resource assignment, SPS-RNTI is used.
In LTE, SPS activation signaling can be made using the PDCCH to initialize an SPS resource. Conversely, SPS release signaling is used to release the SPS resources, and may also be made using the PDCCH. When the PDCCH is used for SPS activation signaling or SPS release signaling, the PDCCH signaling may carry fields that are set to fixed bits to reduce a false alarm probability of the SPS activation and/or release messages. These fixed-value fields act as a redundancy check or checksum and may be referred to as a “Virtual CRC.” In the case of SPS resource allocation, the communication industry has settled on ways to activate and reconfigure SPS resources. Unfortunately, the industry has not developed a reliable way to cause a UA to activate SPS resources that prevents improper allocation of resources when a control channel message is incorrectly received by a UA resulting in a ‘false-alarm’ condition.